CN116608367A - Insulation structure and method for external sliding prefabricated overhead insulation pipe joint - Google Patents

Abstract

The invention discloses a thermal insulation structure and method of an external sliding prefabricated overhead thermal insulation pipe joint, belonging to the technical field of pipeline thermal insulation. Insulation structure includes working tube, soft insulation layer, rigid splicing insulation layer, polyurethane insulation layer, elastic insulation gasket, elastic composite insulation ring, external protection layer, interface section, composite rigid insulation ring, fixed insulation ring, sealing Waterproof casing, sealant and metal outer sheath. The present invention can overcome the problem of serious heat loss at the joint of the finished heat preservation pipe, by using an elastic heat insulation gasket and a composite elastic heat preservation ring in the heat preservation ring at the welding joint of the pipe, perfecting the gap caused by expansion when the pipe joint is heated In addition, it avoids the heat of the working tube from being directly transferred to the outer protective layer through the natural convection of the air in the gap, enhances the thermal insulation performance at the joint of the thermal insulation pipeline, improves the overall thermal economy of the thermal insulation pipeline, and has a good performance in the field of thermal insulation of the pipeline joint job prospect.

Description

A thermal insulation structure and method of an external sliding prefabricated overhead thermal insulation pipe joint

technical field

The invention belongs to the technical field of pipeline heat preservation, and in particular relates to a heat preservation structure and method of an external sliding prefabricated overhead heat preservation pipe joint.

Background technique

With the emphasis on environmental protection from all walks of life, the small coal-fired boilers used for district heating will be gradually dismantled, and the required heat energy will be centrally supplied by large power plants using long-distance heating networks, and the heating radius of the heat transmission pipe network will continue to increase , the heat loss of pipeline insulation has become a key factor affecting the economy of heating pipelines. At the same time, as the thermal pipeline is the key core investment equipment of the thermal system, how to improve the thermal insulation effect of the thermal pipeline and reduce the heat loss of the thermal insulation structure is crucial to improving the economy of the thermal system.

In the prefabricated overhead insulation pipe industry, the most commonly used in the market is the external sliding form. This kind of prefabricated thermal insulation pipe presses the entire thermal insulation layer on the working tube through polyurethane high-pressure foaming and thermal insulation limiting device. The working tube and the thermal insulation layer become a tight whole. After the working tube is heated, the thermal insulation layer The tubes are thermally displaced together. This kind of insulation layer and working pipe are integrated, and a single insulation pipe has a very good insulation effect. The tighter the insulation layer, the smaller the heat convection between the insulation pipe and the outside world. Moreover, the structure of the insulation pipe is stable, and the insulation layer is not subjected to additional external force during operation, which can ensure the service life of the pipeline.

However, when the insulation pipe is working, high-temperature steam is introduced into the pipeline. Because the thermal expansion coefficients between the working pipe and each insulation layer are different, the insulation layer is fixed relative to the center of the working pipe, and the working pipe at the interface will elongate, causing the insulation layer and each insulation layer to be fixed. Displacement occurs between the working tubes, and a gap will be formed at the interface, so that the working tubes communicate with the external air and form natural convection. When the gaps of each layer are connected, there will be serious natural convection at the interface, which will greatly increase the heat loss at the interface, and the efficiency between the thermal insulation performance and the entire heating network will also decrease. In the existing pipeline insulation system, the existing pipeline adopts the method of laying insulation layers in sections to form steps to limit natural convection, but this method fails to prevent the generation of gaps, and the effect is not great.

Therefore, from an economic point of view, solving the problem of serious natural convection and large heat loss at the joint of the heat-insulating structure pipe during work can greatly improve the heat-insulating performance and economy of the heat-insulating pipe, and has broad market prospects.

Contents of the invention

The purpose of the present invention is to overcome the problem of serious heat loss at the joint of the finished insulation pipe, and to prevent the gap between the connecting pipe and the outside world at the joint of the insulation pipe, and propose an insulation structure and method for the joint of the external sliding prefabricated overhead insulation pipe.

The concrete technical scheme that the present invention adopts is as follows:

In the first aspect, the present invention provides a thermal insulation structure of an external sliding prefabricated overhead thermal insulation pipe joint, including two thermal insulation pipes to be spliced; the thermal insulation pipe includes a working tube and a thermal insulation module coated on the outer wall of the main body of the working tube, and the thermal insulation module includes The soft insulation layer, several layers of hard spliced insulation layer and polyurethane insulation layer are laid sequentially from the inside to the outside. Both ends of the working pipe are located outside the insulation module; the ends of the two insulation pipes to be spliced together form an interface section; The ends of the two working pipes located at the interface section are connected by welding to form a weld, and the outer wall is provided with a soft insulation layer with the same thickness as the main soft insulation layer and integrated; the soft insulation layer located at the interface section The two ends of the outer wall of the insulation layer are symmetrically laid with a fixed insulation ring centered on the weld, and an elastic composite insulation ring with the same thickness as the fixed insulation ring is installed between the two fixed insulation rings. The outer ends of each fixed insulation ring are respectively Fitted with the hard spliced insulation layer; the outer wall of the elastic composite insulation ring is laid with a composite hard insulation ring that can completely cover it, and the outer wall of the composite rigid insulation ring is at the same level as the outer wall of the main polyurethane insulation layer The two outer ends of the composite rigid thermal insulation ring are respectively connected to the main body thermal insulation module through elastic thermal insulation gaskets, and the thickness of the elastic thermal insulation gasket is the same as that of the composite rigid thermal insulation ring; The outer wall of the thermal insulation module is also provided with a waterproof outer protective layer that can completely cover it. The outer protective layer includes a sealed waterproof sleeve and a metal outer sheath; there is a seal on the outer wall of the composite hard thermal insulation ring and two elastic heat insulation gaskets. The waterproof cover has stretchable folds in the middle of the sealed waterproof cover, and the two ends are respectively located outside the two elastic heat insulation gaskets and fixed by waterproof sealant; the outer cover of the sealed waterproof cover is provided with a metal outer sheath.

Preferably, the material of the soft insulation layer is aerogel, glass fiber or aluminum silicate rock wool.

As a preference, the number of layers of the rigidly spliced thermal insulation layer is at least 3 layers, each layer is arranged with staggered joints, and each layer is spliced with 2-6 pieces.

Preferably, the polyurethane insulation layer has an integrated structure, including polyurethane and foamed silicate insulation materials.

As a preference, the material of the fixed thermal insulation ring is the same as that of the hard spliced thermal insulation layer, and the thickness is n(x-1); wherein, n is the thickness of a single layer of the rigid spliced thermal insulation layer, and x is the total layer of the rigid spliced thermal insulation layer number.

As a preference, the composite rigid thermal insulation ring includes a rigid splicing thermal insulation layer positioned at the inner layer and a polyurethane thermal insulation layer positioned at the outer layer; the rigid spliced thermal insulation layer and the polyurethane thermal insulation layer of the composite rigid thermal insulation ring are respectively connected to the The spliced insulation is the same thickness as the polyurethane insulation.

Preferably, the materials of the elastic composite thermal insulation ring and the elastic heat insulation gasket are nanoporous airgel felt, elastic ceramic foam, high temperature resistant graphene airgel, glass fiber cotton felt or high temperature resistant foamed silica gel.

Preferably, the axial length of the outer protective layer is 1.5 to 2.0 times the theoretical extension length of the interface section in a hot state.

Preferably, the two insulation pipes located at the interface section are arranged coaxially.

In the second aspect, the present invention provides a method for installing the thermal insulation structure of the outer sliding prefabricated overhead thermal insulation pipe joint as described in any one of the first aspect, specifically as follows:

The ends of the two working pipes are connected by welding, and the strength test after welding and the anti-corrosion of the weld seam at the interface are completed;

In the cold state, a soft insulation layer with the same thickness as the main soft insulation layer is laid on the outer wall of the working tube of the interface section in advance, and the two ends of the soft insulation layer of the interface section are respectively connected to the main soft insulation layer on the two working tubes. The thermal insulation layer is in contact with each other and forms an integrated structure;

In the hot state, fixed insulation rings are laid on both sides of the outer wall of the soft insulation layer of the interface section, and an elastic composite insulation ring with the same thickness as the fixed insulation ring is laid in the middle of the two fixed insulation rings; Elastic heat insulation gaskets are respectively arranged on both sides of the outer wall of the ring, and a composite hard heat insulation ring of equal thickness is laid in the middle of the elastic heat insulation gasket and pressed tightly to form the insulation module structure of the interface section; the insulation module structure of the interface section After the arrangement is completed, the reflective layer and steel belt are used for fixing, and waterproof measures are taken at the interface; then, a sealed waterproof sleeve is arranged on the outside of the elastic heat insulation gasket and the composite hard insulation ring, and the sealed waterproof sleeve uses sealant to connect with the main body on both sides. The polyurethane insulation layer is tightly bonded to completely seal the insulation module of the interface section; then a metal outer sheath is set on the outer layer of the sealed waterproof casing for protection.

Compared with the prior art, the present invention has the following beneficial effects:

(1) The thermal insulation structure of each layer of the present invention is designed with staggered joints, and the same thermal insulation layer staggered joints as the thermal insulation layer of the prefabricated thermal insulation pipe are achieved, which prevents heat convection and heat dissipation inside and outside the thermal insulation layer to the greatest extent.

(2) The present invention uses the design of adding an elastic heat insulation gasket and an elastic composite heat preservation ring to the heat preservation module at the interface, and uses the good elasticity of the material to make up for the gap formed by the uneven thermal expansion of the material at the interface of the traditional heat preservation pipe during work. , enhance the thermal insulation performance at the joint of the thermal insulation pipe, and improve the overall thermal economy of the thermal insulation pipe.

(3) The installation and disassembly of the thermal insulation structure at the interface is simple and convenient: it can be installed according to the drawing; Insulation ring, elastic composite insulation ring and soft insulation layer can inspect the weld.

(4) There is a sealed waterproof sleeve on the outer side of the thermal insulation interface, and it is fixed with high-strength waterproof sealant, which has excellent waterproof performance.

Description of drawings

Fig. 1 is a side sectional view of the thermal insulation structure of the present invention;

Fig. 2 is the schematic diagram of interface section of the present invention;

Fig. 3 is the installation schematic diagram of heat preservation structure of the present invention;

Fig. 4 is a detailed schematic view of the outer protective layer of the present invention.

In the figure: working pipe 1, soft thermal insulation layer 2, hard spliced thermal insulation layer 3, polyurethane thermal insulation layer 4, elastic thermal insulation gasket 5, elastic composite thermal insulation ring 6, outer protective layer 7, interface section 8, weld seam 9 , Composite rigid thermal insulation ring 10, fixed thermal insulation ring 11, sealed waterproof cover 12, fold 13, sealant 14, metal outer sheath 15.

Detailed ways

The present invention will be further elaborated and illustrated below in conjunction with the accompanying drawings and specific embodiments. The technical features of the various implementations in the present invention can be combined accordingly on the premise that there is no conflict with each other.

It should be noted that the "outer wall" mentioned in the present invention refers to the radially outward side of the insulation pipe unless otherwise specified. The "end side" mentioned in the present invention refers to the end along the axial direction of the insulation pipe unless otherwise specified. The "layer" mentioned in the present invention refers to a ring structure unless otherwise specified.

As shown in Figures 1 and 2, it is a thermal insulation structure of an external sliding prefabricated overhead thermal insulation pipe joint provided by the present invention. axis settings. The heat preservation pipe includes a working pipe 1 and a heat preservation module, wherein the heat preservation module is coated on the outer wall of the main body of the work pipe 1 . The thermal insulation module includes a soft thermal insulation layer 2 laid from the inside to the outside, several layers of hard spliced thermal insulation layers 3 and polyurethane thermal insulation layers 4, each layer of thermal insulation layer is a ring structure and is set sequentially. The two ends of the working tube 1 leak out of the insulation module, that is, they are located outside the insulation module; in addition, the ends of the hard spliced insulation layer 3 except the outermost layer are sunken inwards, so as to facilitate the assembly of the insulation module at the joint. As shown in FIG. 2 , the ends of the two insulation pipes to be spliced jointly form an interface section 8 . The present invention also mainly improves the thermal insulation module of the interface section 8, and improves the thermal insulation sealing performance of the interface section, specifically as follows:

The adjacent ends of the two working pipes 1 located at the interface section 8 are connected by welding to form a weld 9, and a soft insulation layer 2 is laid on the outer walls of the two working pipes 1 located at the interface section 8, where the The soft thermal insulation layer 2 and the main body soft thermal insulation layer 2 have the same thickness and are integrally arranged. The integrated layout here means that the two ends of the soft insulation layer 2 of the interface section 8 are in contact with the end sides of the two main body soft insulation layers 2 respectively, and the gap at the contact point is as small as possible; The quality insulation layer 2 can be disassembled separately, so that the welding seam 9 can be repaired later. The two ends of the outer wall of the soft thermal insulation layer 2 at the interface section 8 are provided with fixed thermal insulation rings 11, and the two fixed thermal insulation rings 11 are laid symmetrically around the weld seam 9 with a certain interval between them. Elastic composite thermal insulation ring 6 is installed between two fixed thermal insulation rings 11; Side bonding; the outer end sides of the two fixed heat preservation rings 11 are respectively bonded to the hard splicing heat preservation layer 3 .

In this embodiment, the soft insulation layer 2 is preferably made of airgel, glass fiber or aluminum silicate rock wool. The number of layers of the hard spliced insulation layer 3 is at least 3 layers, and the staggered seams are arranged between each layer, and each layer is spliced with 2-6 pieces to ensure a better thermal insulation effect; as shown in Figure 1, it is three layers Hard splicing insulation layer3. The material of the fixed thermal insulation ring 11 is the same as that of the hard spliced thermal insulation layer 3, and the structure is a semi-cylindrical structure with a thickness of n(x-1); wherein, n is the single-layer thickness of the rigid spliced thermal insulation layer 3, and x is the hard spliced thermal insulation layer 3. The total number of layers of the spliced thermal insulation layer 3; that is, the thickness of the fixed thermal insulation ring 11 is the total thickness of the rigid spliced thermal insulation layer of the pipeline minus the thickness of the single-layer rigid spliced thermal insulation layer.

The outer wall of the elastic composite thermal insulation ring 6 is provided with a composite rigid thermal insulation ring 10 capable of completely covering it. Complete coverage here refers to that the axial length of the composite rigid thermal insulation ring 10 is greater than the axial length of the elastic composite thermal insulation ring 6 . The outer wall of the composite rigid insulation ring 10 and the outer wall of the main polyurethane insulation layer 4 are at the same level, that is to say, the outer wall of the composite rigid insulation ring 10 and the outer wall of the main polyurethane insulation layer 4 should be smooth without unevenness. The two outer ends of the composite rigid thermal insulation ring 10 are respectively connected to the main body thermal insulation module through the elastic thermal insulation gasket 5 , and the thickness of the elastic thermal insulation gasket 5 is the same as that of the composite rigid thermal insulation ring 10 .

In this embodiment, the polyurethane insulation layer 4 is an integrally formed structure, which is composed of polyurethane and foamed silicate insulation material. The structure of the composite rigid thermal insulation ring 10 is a semi-cylindrical integrally formed structure, including a rigid spliced thermal insulation layer 3 on the inner layer and a polyurethane thermal insulation layer 4 on the outer layer, and the rigid spliced thermal insulation layer of the composite rigid thermal insulation ring 10 3 and the polyurethane thermal insulation layer 4 are respectively the same thickness as the rigid splicing thermal insulation layer 3 and the polyurethane thermal insulation layer 4 of the main body; Polyurethane thermal insulation layer 4 material with equal thickness of thermal insulation layer 4 is formed by superposition of both. The materials of the elastic composite thermal insulation ring 6 and the elastic heat insulation gasket 5 are preferably nanoporous airgel felt, elastic ceramic foam, high temperature resistant graphene airgel, glass fiber cotton felt or high temperature resistant foamed silica gel.

As shown in FIG. 4 , the outer wall of the thermal insulation module at the interface section 8 is also provided with a waterproof outer protective layer 7 that can completely cover it. The outer protective layer 7 mainly includes a sealed waterproof sleeve 12 and a metal outer protective layer 15 . On the outer walls of the composite hard thermal insulation ring 10 and the two elastic heat-insulating gaskets 5, there is a sealed waterproof sleeve 12, and the middle part of the sealed waterproof sleeve 12 has stretchable folds 13, and the two ends are respectively located outside the two elastic heat-insulated gaskets 5. And fixed by waterproof sealant 14. The outer cover of the sealed waterproof sleeve 12 is provided with a metal outer sheath 15 .

In this embodiment, in order to ensure the absolute sealing of the port, the length of the sealing waterproof sleeve 12 is 1.2 to 1.3 times of the thermal theoretical extension length of the working tube interface (ie, the interface section 8); in order to prevent the sealing waterproof sleeve 12 from being irradiated by ultraviolet rays Aging, the metal outer sheath 15 is 6-10 cm longer than the two ends of the sealed waterproof casing 12 along the axial direction.

As shown in Figure 3, the installation method of the thermal insulation structure of the above-mentioned external sliding prefabricated overhead thermal insulation pipe joint is as follows:

The ends of the two working pipes 1 are connected by welding, and the strength test after welding and the anti-corrosion of the weld seam 9 at the interface are completed.

When in the cold state, lay the soft insulation layer 2 equal to the thickness of the main body soft insulation layer 2 on the outer wall of the working pipe 1 of the interface section 8 in advance, and the two ends of the soft insulation layer 2 of the interface section 8 are respectively connected with two The main body soft insulation layer 2 on the working tube 1 is in contact with and forms an integrated structure. That is to say, when it is in a cold state, the installation of the inner soft insulation layer 2 with the same thickness as the main body is completed at the welding interface in advance.

In the hot state, fixed thermal insulation rings 11 are respectively laid on both sides of the outer wall of the soft thermal insulation layer 2 of the interface section 8, and an elastic composite thermal insulation ring 6 equal in thickness to the fixed thermal insulation ring 11 is laid in the middle of the two fixed thermal insulation rings 11. Arrange elastic thermal insulation gaskets 5 on both sides of the outer wall of the fixed thermal insulation ring 11 and the elastic composite thermal insulation ring 6, and lay a composite rigid thermal insulation ring 10 of equal thickness in the middle of the elastic thermal insulation gasket 5 and press it tightly to form an interface section 8 insulation module structure. This is because, when the working tube is heated, each standard tube has an elongation of ΔL. According to the expansion and contraction mode of the prefabricated insulation pipe, the end of each standard tube will have an elongation of ΔL/2. Due to the elastic heat insulation The gasket 5 and the elastic composite thermal insulation ring 6 need to be in a compressed state during installation, so they need to be installed in a hot state.

After the thermal insulation module of the interface section 8 is arranged, waterproof measures must be taken. The main sources of moisture at the interface of the prefabricated overhead pipes are rainwater and moisture in the air. During the on-site construction, only the compression and sealing of the outer protective layer 7 cannot meet the requirements, and it is necessary to use a reflective layer and a steel belt to fix it, and arrange a sealing waterproof sleeve 12 outside the interface, and use a high-strength sealant for the sealing waterproof sleeve 12 14. It is closely bonded with the outer sheath of the prefabricated pipe on both sides, and the interface insulation layer is completely sealed, which not only plays the role of waterproof, but also plays the role of preventing heat convection. Simultaneously, the sealing waterproof cover 12 is soft, and can be stretched by lamination. The material of the sealed waterproof case 12 is usually high temperature resistant foamed silica gel. Finally, the outer layer of the pipeline is covered with a metal outer sheath 15 for protection.

The present invention can perfectly supplement the gap generated by the expansion of the pipeline when the pipeline is heated through the good stretchability of the elastic composite thermal insulation ring 6 and the elastic heat insulation gasket 5, preventing the heat of the working tube 1 from being directly transferred through the natural convection of the air in the gap To the outer protective layer 7, the heat of the working tube is prevented from being directly transferred to the outer protective layer through the natural convection of the air in the gap, the thermal insulation performance at the joint of the thermal insulation pipeline is enhanced, the overall thermal economy of the thermal insulation pipeline is improved, and the heat preservation at the pipeline interface The field has good job prospects.

The above-mentioned embodiment is only a preferred solution of the present invention, but it is not intended to limit the present invention. Various changes and modifications can be made by those skilled in the relevant technical fields without departing from the spirit and scope of the present invention. Therefore, all technical solutions obtained by means of equivalent replacement or equivalent transformation fall within the protection scope of the present invention.

Claims (10)

1. A thermal insulation structure of an external sliding prefabricated overhead thermal insulation pipe joint, characterized in that it comprises two thermal insulation pipes to be spliced; the thermal insulation tube includes a working tube (1) and a thermal insulation module coated on the outer wall of the main body of the working tube (1) , the thermal insulation module includes a soft thermal insulation layer (2), several layers of hard spliced thermal insulation layers (3) and a polyurethane thermal insulation layer (4) laid sequentially from the inside to the outside, and both ends of the working pipe (1) are located at the thermal insulation layer Outer side of the module; the ends to be spliced of the two thermal insulation pipes jointly form an interface section (8); the ends of the two working pipes (1) located at the interface section (8) are connected by welding to form a weld (9), and the outer wall A soft thermal insulation layer (2) with the same thickness as the main body soft thermal insulation layer (2) is laid; the two ends of the outer wall of the soft thermal insulation layer (2) located at the interface section (8) are welded (9 ) is a centrally symmetrical laying with a fixed thermal insulation ring (11), and an elastic composite thermal insulation ring (6) with a thickness equal to that of the fixed thermal insulation ring (11) is installed between the two fixed thermal insulation rings (11), and each fixed thermal insulation ring The outer end sides of (11) are respectively bonded to the hard splicing insulation layer (3); the outer wall of the elastic composite insulation ring (6) is laid with a composite rigid insulation ring (10) that can completely cover it, The outer wall of the composite hard thermal insulation ring (10) is at the same level as the outer wall of the main polyurethane thermal insulation layer (4); the two outer ends of the composite rigid thermal insulation ring (10) pass through the elastic heat insulation gasket (5) respectively. Connected with the main body heat preservation module, the thickness of the elastic heat insulation gasket (5) is the same as that of the composite hard heat insulation ring (10); The waterproof outer protection layer (7), the outer protection layer (7) comprises sealing waterproof cover (12) and metal outer sheath (15); ) is provided with a sealed waterproof cover (12), the middle part of the sealed waterproof cover (12) has retractable folds (13), and the two ends are respectively located on the outer sides of the two elastic heat-insulating gaskets (5) and passed through the waterproof sealant (14 ) is fixed; the outer cover of the sealed waterproof sleeve (12) is provided with a metal outer sheath (15). 2. The thermal insulation structure of an external sliding prefabricated overhead thermal insulation pipe joint according to claim 1, wherein the material of the soft thermal insulation layer (2) is aerogel, glass fiber or aluminum silicate rock wool class material. 3. The thermal insulation structure of an external sliding prefabricated overhead thermal insulation pipe joint according to claim 1, characterized in that, the number of layers of the hard spliced thermal insulation layer (3) is at least 3 layers, and the joints between each layer are staggered Arrangement, and each layer has 2-6 pieces spliced. 4. The thermal insulation structure of an external sliding prefabricated overhead thermal insulation pipe joint according to claim 1, characterized in that the polyurethane thermal insulation layer (4) is an integrally formed structure, comprising polyurethane and foamed silicate thermal insulation materials. 5. The thermal insulation structure of a kind of external sliding prefabricated overhead thermal insulation pipe joint according to claim 1, characterized in that, the material of the fixed thermal insulation ring (11) is the same as that of the hard spliced thermal insulation layer (3), and the thickness is n(x-1); Wherein, n is the thickness of a single layer of the rigid splicing thermal insulation layer (3), and x is the total number of layers of the rigid splicing thermal insulation layer (3). 6. The thermal insulation structure of an outer sliding prefabricated overhead thermal insulation pipe joint according to claim 1, wherein the composite rigid thermal insulation ring (10) comprises a rigid spliced thermal insulation layer (3) located in the inner layer and The polyurethane thermal insulation layer (4) located on the outer layer; the rigid spliced thermal insulation layer (3) and polyurethane thermal insulation layer (4) of the composite rigid thermal insulation ring (10) are respectively connected with the rigid spliced thermal insulation layer (3) and polyurethane thermal insulation layer of the main body Layer (4) has the same thickness. 7. The thermal insulation structure of an external sliding prefabricated overhead thermal insulation pipe joint according to claim 1, characterized in that, the materials of the elastic composite thermal insulation ring (6) and the elastic heat insulation gasket (5) are nanopores Airgel felt, elastic ceramic foam, high temperature resistant graphene aerogel, glass fiber cotton felt or high temperature resistant foamed silica gel. 8. The thermal insulation structure of an external sliding prefabricated overhead thermal insulation pipe joint according to claim 1, characterized in that, the axial length of the external protective layer (7) is the theoretical extension length of the interface section (8) in thermal state 1.5 to 2.0 times. 9. The thermal insulation structure of an external sliding prefabricated overhead thermal insulation pipe joint according to claim 1, characterized in that the two thermal insulation pipes located at the interface section (8) are arranged coaxially. 10. An installation method of the thermal insulation structure of the outer sliding prefabricated overhead thermal insulation pipe joint according to any one of claims 1 to 9, characterized in that, the details are as follows: The ends of the two working pipes (1) are connected by welding, and the strength test after welding and the anti-corrosion of the weld (9) at the interface are completed; In the cold state, a soft insulation layer (2) with the same thickness as the main soft insulation layer (2) is laid on the outer wall of the working pipe (1) of the interface section (8) in advance, and the interface section (8) is soft The two ends of the thermal insulation layer (2) are in contact with the main soft thermal insulation layers (2) on the two working tubes (1) respectively to form an integrated structure; In the hot state, lay fixed insulation rings (11) on both sides of the outer wall of the soft insulation layer (2) of the interface section (8), and lay a fixed insulation ring (11) in the middle of the two fixed insulation rings (11), etc. The thickness of the elastic composite thermal insulation ring (6); the elastic thermal insulation gasket (5) is respectively arranged on both sides of the outer wall of the fixed thermal insulation ring (11) and the elastic composite thermal insulation gasket (6), and the middle of the elastic thermal insulation gasket (5) is laid Composite hard thermal insulation rings (10) of equal thickness are compressed to form the thermal insulation module structure of the interface section (8); Fix it, and take waterproof measures for the interface; then arrange a sealed waterproof cover (12) on the outside of the elastic heat insulation gasket (5) and the composite hard thermal insulation ring (10), and use a sealant (14) for the sealed waterproof cover (12) It is tightly bonded to the polyurethane insulation layers (4) of the main bodies on both sides, and the interface section (8) insulation module is completely sealed; then a metal outer sheath (15) is sheathed on the outer layer of the sealed waterproof casing (12) for protection.